Create bulk extension for pre-made accounts and link them?

Doing a trial install of free pbx, and we have freepbx synching with AD and it has pulled in all the accounts already.

I’m trying to do a bulk import of a csv file and create extensions for all our users.
That seems to work fine, all extensions get created, but how do I link those extensions to the already created users automatically?
Or do I need to do it all manually?